Primer



C. A. MARTIN July 15, 1947.

PRIMER Filed Feb. 26, 1942 3mm .Martin Patcnted July 15, 1947 UNITED STATES PATENT OFFICE ranunn Carl A. Martin, Negaunee, Mich.

Application February 26, 1942, Serial No. 432,413

(Granted under the act of March 3, 1883, as amended April 30. 192s; 370 0. o. 157) 6 Claims.

The invention described herein may be manulectured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a primer for explosive charges and more particularly to a cartridge primer for use in ammunition components.

It is a well known fact that, with any firearm or low explosive blasting charge the efiiciency of operation is directly dependent upon the speed and uniformity with which the ignition of the explosive charge is eflected.

It istherefore an object of this invention to increase the efliciency of ignition of explosive charges.

It is a further object to produce, in a primer or charge igniter, a protective Or sealing member which serves to increase the efiiciency of ignition of the charge.

My invention is best carried out in practice by the provision of a disc, sheet, plug, foil'or powder of a low melting alloy, associated with the primer in such a manner as to be subject to the heat of combustion of the priming charge. Upon firing, the low melting alloy will be liquefied and incandescent droplets thereof will be disseminated throughout the charge to be ignited. By so distrlbuting through the charge a plurality of sources of radiant energy, the burning of the charge may be caused to spread from each of the energy sources thus resulting in faster and more uniform ignition of the charge.

The term low melting alloys a used above refers generally to those alloys having a melting point below that of pure tin, 232 C. The low melting or fusible alloys usually consist of binary, ternary, or quaternary mixtures of bismuth, cadmium, lead, or tin in a variety of combinations. It has long been recognized that the binary eutectic has a lower melting point than either of its constituent metals and that the further addition of one or more other low melting metals may result in the forming of a polynary eutectic havmg a still lower melting point. A typical example 01 such combinations is DArcets alloy, a ternary alloy composed of bismuth, parts; lead, 25 parts, and tin, 25 parts. This alloy has a melting point of 93.0 C. Woods metal, a typical quaternary alloy has the composition bismuth, 50 parts; cadmium, 12.5 parts; lead, 25 parts, and tin, 12.5 parts. Woods metal melts at 68 C. Various other combinations having melting points below the boiling Point of water, 100 C., are possible and it is with the group of such alloys which are solid at temperatures which may be reached in air un- 2 der any conditions of storage, and fusible below the boiling point of water that this invention is primarily concerned.

The exact nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

Figure 1 is a longitudinal sectional view of a portion of a cartridge hea including a primer embodying my invention.

Figures 2 to 4 are similar views showing modifications of my invention.

Figure 5 is a similar view showing the application of my invention to a type primer in which an anvil is integrally formed in the primer pocket.

Figure 6 is a longitudinal sectional view of a blasting charge igniter constructed according to my invention.

Referring to the drawing by characters of reference there is shown in Fig. l a portion'of the head of a cartridge I having formed therein a primer pocket 2 and a vent 3 communicating between the primer pocket 2 and the interior of the cartridge case I. Seated in the base of the primer pocket and secured therein by clamping engagement between the bottom of the pocket and a conventional primer 4 is a disc or sheet 5 of one of the fusible alloy compositions discussed above. Under storage conditions this disc of fusible alloy foil will have high stability and will effectively protect the priming composition against the effects of moisture or against the desensitizing effects of certain volatile constituents of the powder mixtures. Upon firing of the primer the fusible disc will be liquefied by the heat generated, a jet of molten particles will be impelled throughout the propellent charge, and ignition thereof may proceed from each of the scattered individual sources of radiant energy thus provided within the cartridge case.

Figure 2 illustrates a modified form in which the fusible alloy is applied as a sealing foil 6 in the manufacture of the primer 4a and is confined between the priming charge I and the anvil 8. This modification will operate as described above.

Figure 3 illustrates a modification in which a.

fusible alloy powder 9 is confined in the primer 1 pocket 2b between the anvil 8b of the primer 4b and a disc 5b of fusible foil. In this form an additional supply of the fusible metal is provided for dissemination through the main charge. In

other respects its operation is as above described.

municating between the primer pocket 20 and the main charge chamber in the case la. The heat generated by the priming charge will melt the fusibleplug and impel the droplets thereof into the main charge chamber.

Figure shows the application of my invention to a cartridge l I of the type formed with an integral anvil I! in the primer pocket l3. A plurality of vents H are provided to carry the primer flame to the main charge chamber. A primer I5 is seated in the pocket l3 and an annular washer l6 of fusible alloy is provided to seal the flash passages M. The drawing shows a quantity of fusible alloy powder I] confined between the primer and the washer IE but this may not always be necessary. The operation of this modification will be the same as of those modifications previously discussed.

Figure 6 shows a blasting charge igniter for low explosives such as the stick or pelleted black powders. This igniter is in most respects of conventional construction, differing in that the shell l8 has been formed open at both ends and has been provided with a closure I! at its lower end. This closure comprises an indented disc of a low melting alloy which may be sealed in moisture proof relation by fusing the disc to the shell or with a solder of an alloy of still lower melting point. Charged against the closure disc is a quantity of fusible metal powder 20. The remainder of the shell is occupied by a charge 2| of deflagrating powder and a conventional igniter charge 22. A rubber plug 23 may conveniently serve as a closure and as a support for the leg wires 24 supporting the bridge wire 25. The charge 2|, which may conveniently be black powder, is ignited in the usualxmanner and the heat develope thereby almost immediately melts the closure member. I9 and powder charge 20. Fusion will proceed from the indented tip of the closure and the molten incandescent metal will be thrown in a powerful stream through the charge, each incandescent droplet serving as a new center for spreading ignition through the charge. In addition to controlling the point at which fusion of the closure will commence the indented structure of the closure disc will add sufiicient strength to the thin closure of relatively weak metal to enable it to withstand any normal abuse in storage and handling.

Particularly in connection with the use of my improved primer in firearms it should be noted thatany solid metallic fouling which may be formed on the walls of the bore by the fusible metal constituents of the primer will be readily melted and removed by cleaning the bore with a hot solution as is normally done to remove the solubl powder fouling. As is noted in Marshall on,Explosives, page 518, vol. II, Second edition 1917, the use of foiled caps of the conventional type is apt to cause the formation of a solid metal fouling in the bore of the rifle unless a considerable excess of oxidizer be used in the cap. As the presence of excess oxygen results in excessive barrel wear it is obvious that this factor alone is an important argument in favor of using the fusible metal foil as a seal, regardless of its other good qualities, as the fouling otherwise formed by the conventional foil seal can only be removed by the action of strong chemical solutions.

It is recognized [that primer compositions comprising powdered metals have been used but such compositions are distinguishable from this invention in that their metallic constituent enters directly into the reaction, serving as a fuel which combines readily with an oxidizing agent provided in the mixture. The instant invention is not concerned with that type of charge as for my purposes it is desirable that the metal be sprayed in molten or semi-molten form through the main charge. Accordingly, in my invention metals of the low fusible type, as distinguished from the highly exothermically reacting metals such as aluminum and magnesium, have been employed. The relatively low latent heat of fusion of the metals of the low melting group insures that they will liquefy and be sprayed upon the main charge in molten or semi-molten form without igniting in the solid state.

I claim:

1. In a cartridge having a primer and a main charge, separating means between said primer and said charge,,said separating means comprising a low melting alloy fusible at a temperature below C.

2. In a cartridge primer pocket having flash passages communicating with the main charge chamber, a sealing'member of a low melting alloy fusible below 100 C. covering said flash passages.

3. In a cartridge havin a primer pocket, a primer therein, and flash passages communicating with the main charge chamber, sealing members of a low melting alloy fusible below 100 C. closing said flash passages, and a quantity of finely divided low melting alloy fusible below 100 C. confined in said primer pocket between said primer and said sealing members.

4. In a charge igniter for igniting a main charge, a primary charge and a quantity of finelydivided low melting alloy fusible below 100 C. adjacent said primary charge and intermediate the same and the main charge, said low melting alloy being adapted to bedistributed within the main charge to ignite the same when said primary charge is ignited.

5. In an explosive charge igniter for a main charge, the combination of a primary charge, a finely-divided low melting alloy fusible below 100 C. superimposed on said priming charge and intermediate the same and the main charge, said low melting alloy being adapted to be dispersed in molten form through the main charge by the firing of the primary charge.

6. An igniter for a charge comprising a receptacle, an indented sealing member therefor of an alloy fusible below 100 C. and a quantity of finelydivided alloy fusible below 100 C. superimposed thereon and contacting the charge, said sealing member and finely divided alloy being adapted to be dispersed in molten form through the charge for igniting the same.

CARL A. MARTIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,188,760 Richardson Jan. 30, 1940 2,095,302 Woodford Oct. 12, 1937 2,127,603 Jones Aug. 23, 1938 FOREIGN PATENTS Number Country Date 23,366 Great Britain Oct. 29, 1904 

